1. Field of the Invention
The present invention relates to an analog-to-digital (A/D) conversion circuit, which converts an analog signal into a digital signal, and a signal processing circuit and a shake detection device using the same.
2. Description of the Related Art
Japanese Patent No. 3064644 discloses an A/D conversion circuit, which inputs a pulse signal into a pulse transit circuit in which a plurality of delay units are connected in series to delay the input pulse signal by a delay time corresponding to an analog signal and output the delayed pulse signal, latches an output signal from each delay unit at a predetermined timing, and generates a digital signal indicating an arrival position of the pulse signal within the pulse transit circuit based on the level of each output signal latched. Japanese Patent No. 3876483 discloses a pressure sensor apparatus, which processes a plurality of analog signals having a correlation using the A/D conversion circuit.
An analog signal input to the pressure sensor apparatus includes a different noise component depending on a timing when an A/D conversion is performed. Thus, if a plurality of analog signals having a correlation are intended to be accurately A/D-converted, it is preferable to simultaneously A/D-convert the plurality of analog signals using A/D conversion circuits of which the number is equal to or greater than the number of analog signals. The A/D conversion accuracy of the above-described A/D conversion circuits largely depends on the performance of the pulse transit circuit. However, the pulse transit circuit includes a negative AND circuit (NAND), inverters (INVs), and the like. Thus, A/D conversion errors easily occur due to individual differences of the A/D conversion circuits.
Accordingly, the above-described pressure sensor apparatus, does not A/D-convert a plurality of analog signals having a correlation during the same period. Thus, it is difficult to reduce the influence of noise components overlapping analog signals during the same period. When A/D conversion circuits of which the number is equal to or greater than the number of analog signals having a correlation are provided and the analog signals are A/D-converted during the same period, it is difficult to reduce the influence of A/D conversion errors due to individual differences of the A/D conversion circuits.